1. Field of the Invention
This invention relates to a CDMA (Code Division Multiple Access) mobile telecommunication method and system, and more particularly to a hand-over method on a control channel in a CDMA mobile telecommunication method and system.
2. Description of the Related Art
As a publication relating to the technical field to which the present invention belongs, TIA (Telecommunications Industry Association), EIA (Electronic Industries Association), IS-95-A, published May, 1995 and so forth are referred to.
Various multiple access systems are adopted for a mobile telecommunication system such as a cellular system. A code division multiple access (CDMA) mobile telecommunication system which is one of the multiple access systems is a system wherein, in order to identify an area called cell covered by each radio base station, a unique spread code is allocated to each radio base station and a same carrier frequency is used in all areas.
In the CDMA mobile telecommunication system, a mobile station first searches cell identification signals transmitted from radio base stations and selects one of the radio base stations which exhibits the highest signal strength.
Then, in order for the mobile station to talk, it communicates control channel signals such as an origination signal or a page response signal using a control channel of the selected radio base station. Then, after the base control station confirms that the mobile station can enjoy a service by the self system, it allocates a traffic channel for talking to allow the mobile station to enter a conversation condition.
The conventional system described above, however, has a problem in that, when a mobile station is present in a boundary region of an adjacent cell, a channel used for transmission by the adjacent cell (for example, a pilot channel by which a cell identification signal is transmitted, a control channel or a traffic channel) so interferes with communication of the mobile station that the mobile station cannot receive a control channel signal of the cell in which the mobile station is present or a traffic channel signal immediately after a traffic channel is allocated.
It is an object of the present invention to provide a CDMA mobile telecommunication method and system which provides augmented ratios of reception of a control channel used between a mobile station present in a boundary region of an adjacent cell and a radio base station and a traffic channel signal immediately after use of a traffic channel is started to raise the call connection completion ratio.
In order to attain the object described above, according to an aspect of the present invention, there is provided a CDMA mobile telecommunication method for a CDMA mobile telecommunication system wherein a plurality of radio base stations are disposed under one base control station and a control channel signal and a traffic channel signal from the base control station are communicated between the radio base stations and a mobile station, comprising the steps of transmitting, when a call is to be connected, an origination signal or a page response signal to which signal strength information of an adjacent cell is added from the mobile station to a particular one of the radio base stations which exhibits the highest signal strength, transmitting, when the base control station receives the origination signal or page response signal from the mobile station through the particular radio base station, control channel information used by the particular radio base station from the base control station to a radio base station of the adjacent cell if the base control station discriminates from the signal strength information of the adjacent cell included in the origination signal or page response signal that the mobile station is present in a boundary region of the adjacent cell, starting, when the radio base station of the adjacent cell receives the control channel information from the base control station, communication of the control channel by the radio base station of the adjacent cell in accordance with the control channel information, transmitting, when the base control station is to transmit a descending control channel signal to the mobile station, the descending control channel signal from the base control station to the particular radio base station and the adjacent radio base station, transmitting, when each of the particular radio base station and the radio base station of the adjacent cell receives an ascending control channel signal from the mobile station, the ascending control channel signal with a signal quality of the received ascending control channel signal added to the ascending control channel signal from the radio base station and the radio base station of the adjacent cell to the base control station, and selecting, by the base control station, one of the ascending control channel signals received through the particular radio base station and the radio base station of the adjacent cell based on the signal qualities of the ascending control channel signals.
When the base control station is to designate a traffic channel for said mobile station which is communicating the control channel signal with the particular radio base station and the radio base station of the adjacent cell, the base control station may cause the particular radio base station and the radio base station of the adjacent cell to start up a traffic channel so that traffic channel designation signals of the particular radio base station and the radio base station of the adjacent cell are transmitted to the mobile station.
According to another aspect of the present invention, there is provided a CDMA mobile telecommunication system wherein a plurality of radio base stations are disposed under one base control station and a control channel signal and a traffic channel signal from the base control station are communicated between the radio base stations and a mobile station, comprising means provided on the base control station for discriminating, when an origination signal or a page response signal from the mobile station is received through a particular one of the radio base stations, from signal strength information of an adjacent cell included in the origination signal or page response signal, whether or not the mobile station is present in a boundary region of the adjacent cell and transmitting, if the base control station discriminates that the mobile station is present in the boundary region of the adjacent cell, control channel information used by the particular radio base station to a radio base station of the adjacent cell, means provided on the radio base station of the adjacent cell for starting, when the control channel information is received from the base control station, communication by a control channel in accordance with the control channel information, means provided on the base control station for transmitting, when the base control station is to transmit a descending control channel signal to the mobile station, the descending control channel signal to the particular radio base station and the adjacent radio base station, means provided on each of the particular radio base station and the radio base station of the adjacent cell for transmitting, when an ascending control channel signal from the mobile, station is received, the ascending control channel signal with a signal quality of the ascending control channel signal added to the ascending control channel signal to the base control station, and means provided on the base control station for selecting one of the ascending control channel signals received from the particular radio base station and the radio base station of the adjacent cell based on the signal qualities of the received ascending control channel signals.
With the CDMA mobile telecommunication method and the CDMA mobile telecommunication system, the mobile station present in the boundary region of the adjacent cell is put into a soft hand-off state on the control channel, and a conversation condition is entered while the state is kept. Consequently, even if interference from the adjacent cell occurs, the call connection completion ratio of the mobile station can be enhanced without deterioration of the reception ratios of a control channel signal and a traffic channel signal immediately after use of the traffic channel is started.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols.